In the formation of color photographic paper it is known that the base paper has applied thereto a layer of polymer, typically polyethylene. This layer serves to provide waterproofing to the paper, as well as providing a smooth surface on which the photosensitive layers are formed. The formation of a suitably smooth surface is difficult requiring great care and expense to ensure proper laydown and cooling of the polyethylene layers. The formation of a suitably smooth surface would also improve image quality as the photographic paper would have more apparent blackness as the reflective properties of the improved base are more spectral than the prior materials. As the whites are whiter and the blacks are blacker, there is more range in between and, therefore, contrast is enhanced.
Prior art imaging reflective papers comprise a melt extruded polyethylene layer which also serves as a carrier layer for optical brightener and other whitener materials as well as tint materials. It would be desirable if the optical brightener, whitener materials and tints, rather than being dispersed throughout the single layer of polyethylene could be concentrated nearer the surface of the layer where they would be more effective optically. The desired attributes of a quality, high impact photographic print materials are a slight blue density minimum, durability, sharpness, and flatness. Cost is also important, as print materials with a polyester substrate tend to be expensive compared with conventional material technology, mainly resin coated paper. For print materials where high levels of durability is needed, traditional color paper is undesirable, as it suffers from a lack of durability for the handling, photographic processing.
In has been proposed in U.S. Pat. No. 5,888,643 that a photographic imaging element comprising a laminated base sheet of paper with a biaxially oriented sheet within a range of Young's modulus be used to control the bending stiffness of said imaging element. While this work provides improved stiffness at a given thickness, it would be useful to provide a photographic imaging element with improved tear resistance. Having a paper base in an imaging element is desirable for it pleasing feel and its cost advantage over plastic bases. One of the disadvantages of a paper base in an imaging element is that it tends to tear easily.
In U.S. Pat. No. 5,866,282 (Bourdelais et al.) it is disclosed that by using microvoided biaxially oriented polyolefin sheets to a cellulose base paper where improved durability is achieved over prior art polyethylene cast coated photographic paper support materials. While this invention does provide improved durability over prior art materials there is a continuing need for tear resistant improvements to improve image durability. Further, improvements in support durability will allow more efficient web transport and stack picking in digital printing equipment such as ink jet printers.
In U.S. Pat. No. 5,866,282 (Bourdelais et al.) white pigments such as TiO.sub.2 are added to the biaxially oriented polyolefin sheet to provide image whiteness and sharpness. While the TiO.sub.2 added to the biaxially oriented sheet does improve whiteness and sharpness compared to melt cast polyethylene imaging supports, there exists a processing limit to the amount of TiO.sub.2 added to polyolefin sheets. Problems such as extrusion die lines, unwanted voiding during orientation and moisture streaks. It has been found that increasing the weight percent of white pigments improves image whiteness, sharpness and opacity.
In U.S. Pat. No. 5,866,282 (Bourdelais et al.) biaxially oriented sheets are laminated to a base cellulose paper for use as a photographic support material. The biaxially oriented sheets described in U.S. Pat. No. 5,866,282, while tear resistant, could be improved by lowering the energy to break to allow for more efficient photographic processing. A lower energy to break would allow for the punching and chopping common to photographic processing operations to be carried out more efficiently as the cutting and punching mechanism would require less force to fracture the biaxially oriented sheets.
In U.S. Pat. No. 3,944,699 biaxially oriented polyester sheets are laminated to cellulose paper as a base for photographic prints. While the lamination of the polyester sheets does provide tear resistance, the support described in U.S. Pat. No. 3,944,699 is not suitable for a photographic print material because the paper base utilized is not sufficiently smooth, the backside film is not rough to ensure efficient web conveyance in photographic processing equipment, to obtain emulsion adhesion, expensive primer coatings are required, no compensating force exists to resist the contraction of the gelatin emulsion at relative humidity less than 50% RH and the neutral areas of the print material would appear undesirably yellow as no attempt was made to compensate for the yellowness of the gelatin commonly utilized in silver halide imaging layers.